This invention relates to a pressure control valve for an open hydraulic circuit, in which the control action is provided by feeding to discharge a predetermined proportion of the flow of fluid fed to the valve.
Valves of this type comprise a mobile valve element arranged to open a discharge port in order to discharge said proportion of flow, its movement being controlled by a servomechanism controlled normally by an electromagnet.
This servomechanism, which is usually of hydraulic operation, acts as an actual amplifier in order to generate forces and/or movements which are sufficiently large to control said valve element, when much smaller forces and/or movements are applied to or induced in said servomechanism.
Because of the structure of said servomechanism, valves of the described type are constructionally rather complicated, of large overall size and sometimes of low reliability.
Furthermore, they have poor versatility of application because each valve can be used only for pressures lying within a well defined range.